JPH11135003A - Photoelectric surface and electron tube using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photoelectric surface provided with a light absorption layer having little crystalline defect, and highly sensitive against visible light and infrared rays of an arbitrary wave length zone, and provide an electron tube using it. SOLUTION: A light absorption layer 11 comprising Be doped (p) type Ga1-x Inx Ny As1-y of carrier concentration of 1×10<18> cm<-3> and of 2 μm thick, an electron carrying layer 12 comprising Be doped (p) type GaAs of carrier concentration of 1×10<19> cm<-3> and of 0.5 μm thick, and an extremely thin surface layer 13 comprising Cs2 O for decreasing the work function of the surface are successively formed on a semiconductor substrate 10 comprising semi-insulative GaAs. By selecting the combination of (x) and (y) so that the composition of the Ga1-x Inx Ny As1-y constituting the light absorption layer 11 is respectively lattice matched with the semiconductor substrate 10 and the electron carrying layer 12 and the lattice matching condition of 0.41x-1.14y=0 is satisfied, a lattice constant deviation can be adjusted so as to be within 1%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photocathode, and more particularly to a semiconductor photocathode which emits photoelectrons with high efficiency with respect to light to be detected in an infrared region, and an electron tube using the same.

[0002]

2. Description of the Related Art Among conventionally known III-V group compound semiconductors, GaAs, GaP, GaN or GaAs is used.
Since P has a negative electron affinity, the photocathode provided with it exhibits high photoelectric conversion efficiency. FIG. 10 shows a so-called reflection type photocathode as an example, and GaAs
The light absorption layer 11 made of P-type GaAs is epitaxially grown on the semiconductor substrate 10 made of s. Then, a surface layer 13 made of Cs ₂ O is formed on the surface of the light absorbing layer 11 which has been heated and cleaned in a vacuum vessel (not shown) in order to lower its work function. As a result, a photocathode having relatively high sensitivity up to a wavelength of 900 nm determined by the forbidden band width of the semiconductor used is obtained, and a photomultiplier tube having the photocathode has already been put to practical use.

On the other hand, a wavelength 9 determined by the forbidden band width of GaAs.
FIG. 11 shows an example of a semiconductor photocathode having sensitivity in an infrared wavelength region longer than 00 nm. That is, as shown in FIG. 11, p-type In _1-x Ga _x As _{1-y Py} is epitaxially grown as a light absorbing layer 11 on a semiconductor substrate 10 made of InP, and a surface layer 13 made of Cs ₂ O is further formed. And a photocathode in which a Schottky electrode 14 made of Ag is formed on a part of the surface of the surface layer 13 is described in the literature (JS Escher an.
dR. Sankaran: Applied Physs
ics Letters, Vol. 29, No. 2,
p. 87 (1976)).

However, in order to obtain a relatively high photoelectric conversion efficiency, In _1-x Ga _x A
As s _1-y P _y is nearly lattice matched to the semiconductor substrate 10 made of InP, the composition of which must be in the range of 0 ≦ x ≦ 0.5. In _1-x Ga _x As corresponding to this composition
Bandgap of _1-y P _y is at least 0.7 eV, therefore, the wavelength range of the photocathode to respond was limited to below 1.7 [mu] m. In other composition ranges, a large number of defects are generated in the light absorption layer 11 due to lattice mismatch, which work as recombination centers of electrons, so that the photoelectric conversion efficiency sharply deteriorates.

Further, in the above composition range, In
_{1-x Ga x As 1-} y for P _y is difficult to negatively electron affinity also to form a surface layer 13 consisting of Cs ₂ O, a high is applied to the Schottky electrode 14 made of Ag surface It was necessary to increase the kinetic energy of the electrons by the electric field, transition the electrons from the Г point of the direct transition in the conduction band to a high energy band such as the X point and the L point of the indirect transition, and release the electrons from there. For this reason, the electron emission efficiency was lower than that of a semiconductor having a negative electron affinity.

As shown in FIG. 12, a p.sup. ⁺ Type GaAs is used as a photoemission surface having sensitivity in an arbitrary long wavelength region.
on a semiconductor substrate 10 made of s, it multilayer semiconductor quantum well provided consisting of Al _0.65 Ga _0.35 As62 and undoped GaAs63 Metropolitan lattice-matched as a light absorbing layer 11, p on the light absorbing layer 11 ^- consisting -type GaAs contact A technique in which a layer 64 and a mesh-shaped Schottky electrode 65 are formed is disclosed in Japanese Patent Laid-Open No. Hei 5-234501.

[0007]

However, since it is not possible to efficiently inject electrons from the semiconductor substrate 10 made of p ⁺ -type GaAs into the undoped light-absorbing layer 11, the sub-band is once removed from the quantum well of the light-absorbing layer 11. When photoelectrons are emitted by the transition between layers, there is a problem that it is difficult to continuously operate even if light subsequently enters. Further, since the contact layer 64 made of p ^-- type GaAs has no negative electron affinity, only electrons having higher energy than the vacuum level due to the electric field are emitted to the outside, so that the photoelectron emission efficiency is not so high. There was also a problem.

Accordingly, the present invention provides a p-type Ga _1-x In _x N _y As _1-y or p-type Ga _1-x In _x N lattice-matched to a semiconductor substrate.
_{By using y} P _1-y for the light absorbing layer, the above-described problem is essentially solved, and a highly sensitive photoelectric surface in the wavelength region from visible light to infrared light and an electron tube using the same are provided. is there.

[0009]

According to a first aspect of the present invention, there is provided a semiconductor substrate made of Si, GaAs or GaP, and a p-type Ga _1-x In _x N _y formed on the semiconductor substrate.
A light-absorbing layer which is made of As _1-y or p-type Ga _{1- x} In _x N _y P _1-y and absorbs light to be detected to generate photoelectrons, and is formed on the light absorbing layer; Carrier concentration is 1 × 1
An electron transport layer made of p-type GaAs, p-type GaP or a mixed crystal thereof of at least 0 ¹⁷ cm ^-3 and diffusing photoelectrons generated from the light absorption layer to near the surface; and an alkali metal formed on the electron transport layer. Or a surface layer comprising an oxide or a fluoride thereof and negatively reducing the electron affinity of the electron transport layer.

[0010] The second aspect of the present invention is directed to Si, GaAs.
A p-type Ga _1-x In _x N _y As _1-y or p-type Ga _1-x I formed on a semiconductor substrate made of GaP and a semiconductor substrate;
consists _{n x N y P 1-y} , and the light absorption layer which generates photoelectrons absorbs the light to be detected is detected, is formed on the light absorbing layer, the carrier concentration of least 1 × 10 ¹⁵ cm ^-3 P-type Ga
An electron transporting layer formed of As, p-type GaP or a mixed crystal thereof and diffusing photoelectrons generated from the light absorbing layer to near the surface, and formed on the electron transporting layer, from an alkali metal or an oxide thereof or a fluoride thereof. And a bias voltage such that the electron transport layer has a Schottky junction with the surface layer that negatively reduces the electron affinity of the electron transport layer and the electron transport layer formed on the electron transport layer, and the electron transport layer is positive with respect to the light absorption layer. And an electrode for applying a voltage.

According to a third aspect of the present invention, there is provided a semiconductor device comprising: Si, GaAs;
A p-type Ga _1-x In _x N _y As _1-y or p-type Ga _1-x I formed on a semiconductor substrate made of GaP and a semiconductor substrate;
consists _{n x N y P 1-y} , and the light absorption layer which generates photoelectrons absorbs the light to be detected is detected, is formed on the light absorbing layer, the carrier concentration of least 1 × 10 ¹⁵ cm ^-3 P-type Ga
An electron transporting layer formed of As, p-type GaP or a mixed crystal thereof and diffusing photoelectrons generated from the light absorbing layer to near the surface, and formed on the electron transporting layer, from an alkali metal or an oxide thereof or a fluoride thereof. And a surface layer that negatively lowers the electron affinity of the electron transport layer, and a n-type GaAs, an n-type GaP or a mixed crystal thereof formed on a part of the electron transport layer. A contact layer formed on the contact layer and an electrode for applying a bias voltage so that the electron transport layer is positive with respect to the light absorption layer.

The invention according to claim 4 is characterized in that the lattice constant of the semiconductor substrate, the lattice constant of the light absorption layer, and the lattice constant of the electron transport layer are each matched within a deviation range of 1% or less. I do.

According to a fifth aspect of the present invention, there is provided Ga _1-x In _x N _y As _1-y or Ga _1-x In _x N _y P _1-y forming a light absorption layer.
It is characterized in that the composition y of the medium N satisfies 0 <y ≦ 0.2.

The invention according to claim 6 is characterized in that the forbidden band width of the semiconductor substrate and the forbidden band width of the electron transport layer are both larger than the forbidden band width of the light absorbing layer.

According to a seventh aspect of the present invention, there is provided a vacuum container having an entrance window through which light to be detected is incident, the interior of which is held in a vacuum, and a vacuum container facing the entrance window and housed in the vacuum container. An electron tube comprising the photoelectric surface and an anode housed in a vacuum vessel and maintained at a positive potential with respect to the photoelectric surface.

The invention according to claim 8 is characterized in that it further comprises an electron multiplying unit accommodated in a vacuum vessel and multiplying photoelectrons from the photocathode by secondary electrons.

According to the present invention, no lattice mismatch occurs between the semiconductor substrate and the electron transport layer and the light absorption layer epitaxially grown therebetween. Also, by changing the forbidden band width of the light absorption layer, photoelectrons can be efficiently generated from visible light to an infrared region of 10 μm or more, and the photoelectrons are generated by a so-called interband transition from a valence band to a conduction band. Therefore, it can operate permanently without supplying electrons from outside.

Further, since the electron transport layer has a negative electron affinity, photoelectrons can be emitted to the outside with high efficiency without applying a high bias voltage. Therefore, the photoelectric surface according to the present invention can emit photoelectrons to the outside with high efficiency with respect to the detected light in the wavelength range from visible light to infrared light. Further, the electron tube using the photocathode according to the present invention can convert a photoelectron signal from the photocathode into an electric signal.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a photoelectric surface and an electron tube using the same according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing a photocathode according to the first embodiment of the present invention. A carrier concentration of 1 × 10 ¹⁸ c is formed on a semiconductor substrate 10 made of semi-insulating GaAs.
m ⁻³ , 2 μm thick Be-doped p-type Ga _1-x In _x N _y A
light absorbing layer 11 of s _1-y , carrier concentration 1 × 10 ¹⁹
cm ^-3, an electron transport layer 12 made of Be-doped p-type GaAs having a thickness of 0.5 [mu] m, Cs ₂ O consisting of very thin surface layer 13 for reducing the work function of the surface are successively formed. Here, Ga _1-x In _x N constituting the light absorption layer 11
The composition of _y As _1-y depends on the semiconductor substrate 10 and the electron transport layer 12.
By selecting a combination of x and y so as to lattice-match with GaAs, respectively, and satisfying the lattice-matching condition of 0.41x-1.14y = 0, it is possible to adjust the deviation of the lattice constant within 1%. .

By satisfying this lattice matching condition,
Since almost no defect serving as a recombination center of carriers occurs in the light absorbing layer 11, most of the photoelectrons diffuse into the electron transport layer 12 without being lost. Further, the flat light absorbing layer 11
Can be formed, so that a highly uniform photocathode can be obtained. Further, Ga _1-x In _x N _y As satisfying the lattice matching condition.
The forbidden band width of _1-y and the light wavelength corresponding thereto change with respect to the N composition (N composition) y as shown in FIG. That is, light having energy higher than the forbidden band width is emitted to the light absorbing layer 1.
1, the photocathode according to the present embodiment can detect an arbitrary wavelength region from visible light to infrared light having a wavelength of 10 μm or more by appropriately selecting the composition of x and y. High sensitivity to light.

The N composition y in Ga _1-x In _x N _y As _1- y is 0 <y ≦ 0.2 in order to realize a positive bandgap.
And Further, according to the wavelength to be detected, if 0.3 μm to 2 μm, respectively, 0 <y ≦ 0.1, 2 μm
If m to 5 μm, 0.1 <y ≦ 0.16, 5 μm to 1
If it is 5 μm, it is preferable that 0.16 <y ≦ 0.19. In particular, in the present embodiment, since no external electric field is applied, the sensitivity is high in a wavelength range of 1.2 μm or less, and the corresponding N composition y is 0.045.

The light absorption layer 11 and the electron transport layer 12 are formed by a molecular beam epitaxy (MBE) method or a metal organic chemical vapor deposition (MOVPE) method. As a nitrogen supply source for forming the light absorption layer 11, nitrogen gas is used as a plasma in the MBE method, and NH ₃ or N ₂ H ₄ is used in the MOVPE method.
Is used.

As the p-type doping impurity, Be
Instead, Zn, C or Mg may be used. Light absorbing layer 1
If the carrier concentration of 1 is 1 × 10 ¹⁵ cm ⁻³ or more,
The same effect as described above can be obtained. The thickness of the light absorbing layer 11 is
The thickness only needs to be sufficient to absorb the light to be detected, and may be substantially 1 μm or more. The carrier concentration of the electron transport layer 12 may be 1 × 10 ¹⁷ cm ⁻³ or more so as to obtain a negative electron affinity, and the thickness is substantially 2 μm or less so as to be smaller than the electron diffusion length. Is fine.

The surface layer 13 is formed by forming a light absorbing layer 11 and the electron transport layer 12 on the semiconductor substrate 10, the surface of the electron transport layer 12 is cleaned by heating in vacuum, then Cs and O ₂
Are alternately supplied. Incidentally, as the light absorbing layer 11 may be a p-type _{Ga 1-x In x N y} P 1-y. At this time, the composition of Ga _1-x In _x N _y P _1-y is x, y
0.61x−0.94y = 0.2
By satisfying the lattice matching condition described above, the deviation of the lattice constant can be adjusted to within 1%.

Ga _1-x In _x N satisfying this lattice matching condition
The forbidden band width of _y P _1-y and the corresponding light wavelength change as shown in FIG. 3 with respect to the N composition y. Ga _1-x In _x N
The N composition y in _y P _{1 -y} is set to 0 <y ≦ 0.13 in order to realize a positive bandgap. Further, according to the wavelength to be detected, for example, 0 <y ≦ 0.09 for 0.65 μm to 2 μm and 0.09 for 2 μm to 5 μm, respectively.
<Y ≦ 0.11, 0.15 <5 μm to 15 μm
It is desirable that y ≦ 0.13. In particular, 1.2 μm
In order to obtain high sensitivity in the following wavelength range, the N composition y is set to 0.056.

Furthermore, semi-insulating or high-resistance GaP or Si may be used as the semiconductor substrate 10. In this case, the electron transport layer 12 is p-type GaP. Semiconductor substrate 1
By making 0 a semi-insulating property or a high resistance, free carrier absorption of infrared rays that do not generate photoelectrons can be suppressed. Although the efficiency of photoelectric conversion is slightly lowered, the semiconductor substrate 10
May be p-type. Further, the Si substrate has advantages such as low cost, large area, and high mechanical strength.

When various materials are selected for the semiconductor substrate 10 and the light absorbing layer 11, the respective lattice matching conditions are as follows.
That is, (1) the semiconductor substrate 10 is GaP and the light absorbing layer 1
1 is Ga _1-x In _x N _y As _1-y , the composition is 0.1.
41x-1.14y = -0.2; (2) The semiconductor substrate 10 is Si, and the light absorbing layer 11 is Ga _1-x
The composition of In _x N _y As _1-y is 0.41x-
1.14y = −0.22; (3) The semiconductor substrate 10 is GaP, and the light absorbing layer 11 is Ga.
Composition when formed into a _{1-x In x N y P} 1-y is, 0.44X-
0.94y = 0; and (4) the semiconductor substrate 10 is Si, and the light absorbing layer 11 is Ga _1-x
The composition of In _x N _y P _1-y is 0.44x-0.
94y = −0.02. A combination of x and y that satisfies such a lattice matching condition is selected and adjusted to a deviation of lattice constant within 1%.

In the embodiment shown in FIG. 1, a so-called reflection type photocathode having the same surface on which light to be detected is incident and a surface from which photoelectrons are emitted has been described as an example. It is apparent that the present invention is not limited to the surface, but can be applied to a so-called transmission type photoelectric surface in which the surface on which light to be detected is incident and the surface from which photoelectrons are emitted are different. However, in this case, the light to be detected reaches the light absorption layer 11 via the semiconductor substrate 10. Therefore, the wavelength range in which the photocathode has sensitivity according to the wavelength range of light absorbed by the semiconductor substrate 10 is 0.9 μm or more when GaAs is used for the semiconductor substrate 10.
When P is used, it is limited to 0.55 μm or more, and when Si is used, it is limited to 1.1 μm or more.

FIG. 4 is a schematic sectional view showing a photocathode according to a second embodiment of the present invention. By a method similar to that of the first embodiment, a Be-doped p-type Ga _1-x In _x N _y As ₁ having a carrier concentration of 1 × 10 ¹⁶ cm ⁻³ and a thickness of 2 μm is formed on a semiconductor substrate 10 made of semi-insulating GaAs. _-y light absorbing layer 1
1. An electron transport layer 12 made of Be-doped p-type GaAs having a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ and a thickness of 0.5 μm is sequentially formed.

Further, an Al Schottky electrode 14 is vacuum-deposited on the electron transport layer 12 and processed into a mesh pattern by photolithography to partially expose the surface of the electron transport layer 12. A part of the light absorption layer 11 is exposed by etching, and an AuZn ohmic electrode 15 is formed on the part by vacuum evaporation. Next, in order to lower the work function of the surface, an extremely thin surface layer 1 made of Cs ₂ O is used.
3 is formed in the same manner as in the first embodiment.

The composition of Ga _{1 -x} In _x N _y As _{1 -y} is similar to that of the first embodiment, except that the semiconductor substrate 10 and the electron transport layer 12 have the same composition.
Are selected so as to have a lattice match within 1% of each other. A bias voltage is applied between the Schottky electrode 14 and the ohmic electrode 15 so that the electron transport layer 12 side is positive with respect to the light absorption layer 11. The second thus configured
The photoelectron emission mechanism on the photocathode according to the embodiment will be described below based on the energy band diagram shown in FIG.

When the light to be detected passes through the electron transport layer 12 and enters the light absorption layer 11, photoelectrons are generated due to an interband transition from the valence band to the conduction band. Since the photoelectrons have few defects in the light absorbing layer 11, they are hardly lost by non-radiative recombination. Further, the photoelectrons are accelerated in the direction of the electron transport layer 12 by the electric field applied between the electrodes, and therefore, as compared with the first embodiment, the photoelectrons get over the barrier at the boundary between the light absorption layer 11 and the electron transport layer 12, or Alternatively, the rate of transmission through the tunnel effect to reach the electron transport layer 12 increases. The photoelectrons that have reached the electron transport layer 12 move to the surface side by diffusion or a drift electric field, and the level of the lower end of the conduction band on the surface of the electron transport layer 12 is
Since the level is higher than the vacuum level due to the effect of No. 3, it is easily emitted to the outside.

In the second embodiment of the present invention, by applying a bias voltage, the energy position of the bottom of the conduction band of the light absorbing layer 11 can be changed to that of the electron transporting layer 12 regardless of the forbidden band width of the light absorbing layer 11. Higher, the photoelectrons can be efficiently transferred to the electron transporting layer 12.
This is effective for detecting infrared light having the above wavelengths. In addition,
Also in the second embodiment, similar to the first embodiment,
The semiconductor substrate 10 may be a Si or GaP, optical absorption layer 11 may be a p-type _{Ga 1-x In x N y} P 1-y.
Further, the electron transport layer 12 may be p-type GaP or a mixed crystal of p-type GaAs and p-type GaP. Furthermore, a so-called transmissive photoelectric surface, in which the surface on which the light to be detected is incident and the surface on which photoelectrons are emitted may be different.

The material of the Schottky electrode 14 may be Au or Ti other than Al. Further, the material of the ohmic electrode 15 may be AuCr or InZn other than AuZn. Further, in addition to forming the ohmic electrode 15 in a portion where a part of the light absorption layer 11 is exposed by etching, p-type GaAs or G
The ohmic electrode 15 may be formed on the back surface of the semiconductor substrate 10 using aP or Si.

FIG. 6 is a sectional view showing a photocathode according to a third embodiment of the present invention. By a method similar to that of the first embodiment, a semiconductor substrate 10 made of semi-insulating GaAs is
A light absorption layer 11 made of Be-doped p-type Ga _1-x In _x N _y As _{1 -y having a} carrier concentration of 1 × 10 ¹⁶ cm ⁻³ and a thickness of 2 μm;
Be with a carrier concentration of 1 × 10 ¹⁶ cm ⁻³ and a thickness of 0.5 μm
An electron transport layer 12 made of doped p-type GaAs is formed sequentially.

Further, the carrier concentration is 1 × 10 ¹⁸ cm ^-3 and the thickness is 0.5 μm so as to form a pn junction with the electron transport layer 12.
An n-type GaAs contact layer 16 is formed. Next, an AuGe upper ohmic electrode 17 is vacuum-deposited on the contact layer 16 and processed into a mesh pattern by photolithography and etching to partially expose the surface of the electron transport layer 12.

A part of the light absorbing layer 11 is exposed by etching, and a lower ohmic electrode 18 of AuZn is formed on the exposed part by vacuum evaporation. Next, in order to lower the work function of the surface, an extremely thin surface layer 13 made of Cs ₂ O is formed by the same method as in the first embodiment. The composition of Ga _1-x In _x N _y As _1-y constituting the light absorption layer 11 is the same as that of the first embodiment.
2 is selected so as to be lattice-matched with a deviation within 1%. A bias voltage is applied between the upper ohmic electrode 17 and the lower ohmic electrode 18 so that the electron transport layer 12 side is positive with respect to the light absorption layer 11.

The photoelectron emission mechanism on the photocathode of the third embodiment thus configured is exactly the same as that of the second embodiment. Therefore, the third embodiment has the same effect as the second embodiment. The upper ohmic electrode 17
May be InSn or the like other than AuGe. The material of the lower ohmic electrode 18 is AuZn.
Alternatively, AuCr or InZn may be used.

Further, in addition to forming the lower ohmic electrode 18 at a portion where a part of the light absorbing layer 11 is exposed by etching, a p-type GaAs or G
The lower ohmic electrode 18 may be formed on the back surface of the semiconductor substrate 10 using aP or Si. As described above, the light absorption layer 11 having an arbitrary band gap in which crystal defects are suppressed by lattice matching and the electron transport layer 12 having a negative electron affinity are formed on the semiconductor substrate 10 by epitaxial growth. Therefore, the photocathode according to the present invention can emit more photoelectrons than in the past, particularly for infrared rays having a long wavelength.

Next, an electron tube using a photocathode according to the fourth embodiment of the present invention will be described. FIG. 7 is a schematic plan sectional view showing a so-called circular gauge type photomultiplier tube 100. In FIG. 7, in a cylindrical glass bulb with an entrance window 31 constituting a light-transmissive vacuum vessel 30, it is inclined at a certain angle with respect to the detection light (hν) incident from the entrance window 31. Dynode part 4 comprising a plurality of dynodes 40a to 40h for sequentially multiplying the photocathode 20 thus obtained and photoelectrons emitted from the photocathode 20.
0 and an anode 50 for collecting the output signal.

The photocathode 20 is the same as that of the first embodiment.
3 can be used. Although not shown,
For the photocathode 20, the dynode unit 40, and the anode 50,
Via the bleeder circuit and the electrical leads, a positive bleeder voltage is distributed and applied to the photocathode 20 such that it increases step by step as it approaches the anode 50. Further, the vacuum vessel 30 can be cooled by a Peltier element, liquid nitrogen, or the like to reduce dark current.

The light to be detected that has passed through the entrance window 31 of the vacuum vessel 30 of the photomultiplier tube 100 is applied to the light absorbing layer 11 of the photocathode 20.
And photoelectrons are generated and released into a vacuum. When the emitted photoelectrons are accelerated and incident on the first dynode 40a, multiplied secondary electrons are generated and emitted into a vacuum. The secondary electrons emitted from the first dynode 40a are accelerated again, enter the second dynode 40b, and further generate and emit secondary electrons. By repeating this eight times, the photoelectrons emitted from the photocathode 20 are finally multiplied by about one million times at the eighth dynode 40h and emitted. And the eighth dynode 4
Secondary electrons multiplied from 0h and emitted are collected by the anode 50 and taken out as an output signal current.

In the present embodiment, since the number of photoelectrons emitted from the photocathode 20 is particularly large with respect to infrared rays, the signal current finally output from the anode 50 is also large.
Infrared rays can be detected with higher sensitivity than a conventional circular gauge type photomultiplier tube.

Next, an electron tube using a photocathode according to a fifth embodiment of the present invention will be described. FIG. 8 is a schematic sectional view showing a so-called head-on type photomultiplier tube 200.
8, in a cylindrical glass bulb with an entrance window 31 constituting a vacuum vessel 30, a photoelectric surface 20 arranged perpendicularly to light to be detected (hν) incident from the entrance window 31; A dynode section 40 composed of a plurality of stages of dynodes 40a to 40h for sequentially multiplying photoelectrons emitted from the photocathode 20 and an anode 50 for collecting output signals are arranged.

The photocathode 20 corresponds to the first embodiment.
3 can be used. Although not shown,
For the photocathode 20, the dynode unit 40, and the anode 50,
Via the bleeder circuit and the electrical leads, a positive bleeder voltage is distributed and applied to the photocathode 20 such that it increases step by step as it approaches the anode 50. Further, the vacuum vessel 30 can be cooled by a Peltier element, liquid nitrogen, or the like to reduce dark current.

The light to be detected that has passed through the entrance window 31 of the vacuum vessel 30 of the photomultiplier tube 200 is applied to the light absorbing layer 11 of the photocathode 20.
And photoelectrons are generated and released into a vacuum. When the emitted photoelectrons are accelerated and incident on the first dynode 40a, multiplied secondary electrons are generated and emitted into a vacuum. The secondary electrons emitted from the first dynode 40a are accelerated again, enter the second dynode 40b, and further generate and emit secondary electrons. By repeating this eight times, the photoelectrons emitted from the photocathode 20 are finally multiplied by about one million times at the eighth dynode 40h and emitted. And the eighth dynode 4
Secondary electrons multiplied from 0h and emitted are collected by the anode 50 and taken out as an output signal current.

In the present embodiment, since the number of photoelectrons emitted from the photocathode 20 is particularly large with respect to infrared rays, the signal current finally output from the anode 50 is also large, and the conventional head-on type photoelectron multiplication is increased. Infrared rays can be detected with higher sensitivity as compared with a multiplier.

Next, an electron tube using a photocathode according to the sixth embodiment of the present invention will be described. FIG. 9 is a schematic sectional view showing an image intensifier tube 300 according to the present invention. In FIG. 9, a photocathode 20 and a vacuum chamber 30 having an entrance window 31 are provided.
A microchannel plate (MCP) 51, an electron multiplying unit including input-side and output-side electrodes 52 and 53, and an anode unit including a phosphor screen 54, an electrode 55, and a fiber plate 56 are arranged. The photoelectric surface 20 according to the first to third embodiments can be used as the photoelectric surface 20. Also,
The vacuum vessel 30 can be cooled by a Peltier element, liquid nitrogen, or the like to reduce dark current.

When light to be detected enters the image intensifier tube 300, photoelectrons are emitted and multiplied in the same manner as in the fourth and fifth embodiments of the electron tube according to the present invention.
Photoelectrons emitted from the output surface of the MCP 51
1 is accelerated to enter the phosphor screen 54 to which a more positive voltage is applied, and emits light. That is, the image intensifier tube 3
In 00, a portion of the phosphor screen 54 corresponding to the incident position of the light on the photocathode 20 emits light, so that one-dimensional or two-dimensional position detection and imaging can be performed. The emission of the fluorescent screen 54 can be confirmed through the fiber plate 56, and is particularly suitable for position detection or imaging under low illuminance.

In the present embodiment, in particular, the number of photoelectrons emitted from the photocathode 20 with respect to infrared rays increases.
Infrared rays can be detected with higher sensitivity than a conventional image intensifier tube. The embodiments of the electron tube according to the present invention are not limited to the three embodiments 4 to 6. For example, an electron implantation type photomultiplier using a semiconductor diode in a multiplication unit of a photomultiplier tube. Position-detection-type photomultiplier tubes using multi-channel semiconductor diodes in tubes and photomultiplier tube multipliers, and MCPs for image intensifier tubes
And back-illuminated charge-coupled device (CCD) instead of phosphor screen
The present invention can also be applied to an image intensifier tube using the same. These electron tubes can detect infrared rays with higher sensitivity than before.

[0051]

As described above, according to the present invention, the light absorption layer has an arbitrary band gap, crystal defects are suppressed by lattice matching with the semiconductor substrate, and the electron transport layer has a negative energy. Since the photocathode according to the present invention has an electron affinity, a photocathode having a very high sensitivity can be obtained particularly for infrared rays having a long wavelength. Further, according to the electron tube using the photoelectric surface of the present invention, there is an effect that weak infrared rays having a long wavelength can be detected with higher sensitivity than before.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a photocathode according to a first embodiment of the present invention.

FIG. 2 shows Ga _1-x In _x N _y As lattice-matched to GaAs
FIG. 3 is a diagram showing a relationship between a forbidden band width of _1-y (solid line) and a corresponding light wavelength (broken line) and a composition y.

FIG. 3 shows Ga _1-x In _x N _y P _1-y lattice-matched to GaAs
Band gap (solid line) and corresponding light wavelength (dashed line)
FIG. 4 is a diagram showing a relationship between the composition and the composition y.

FIG. 4 is a schematic sectional view showing a photocathode according to a second embodiment of the present invention.

FIG. 5 is an energy band diagram of a photocathode according to a second embodiment of the present invention.

FIG. 6 is a schematic sectional view showing a photocathode according to a third embodiment of the present invention.

FIG. 7 is a schematic plan sectional view showing an electron tube according to a fourth embodiment of the present invention.

FIG. 8 is a schematic sectional view showing an electron tube according to a fifth embodiment of the present invention.

FIG. 9 is a schematic sectional view showing an electron tube according to a sixth embodiment of the present invention.

FIG. 10 is a schematic cross-sectional view showing a reflective photocathode in which a p-type GaAs light absorbing layer is epitaxially grown on a conventional GaAs substrate.

FIG. 11 is a schematic cross-sectional view showing a conventional photocathode having a p-type In _1-x Ga _x As _{1-y Py} as a light absorption layer.

FIG. 12 is a schematic cross-sectional view showing a conventional photocathode having a quantum well as a light absorbing layer.

[Explanation of symbols]

Reference Signs List 10 semiconductor substrate, 11 light absorbing layer, 12 electron transport layer, 13 surface layer, 14 Schottky electrode, 15 ohmic electrode, 16 contact layer, 17 upper ohmic electrode, 18 lower ohmic electrode, 20 ... Photocathode, 3
0: vacuum vessel, 31: entrance window, 40: dynode part, 4
0a: first dynode, 40b: second dynode, 40
c: third dynode, 40d: fourth dynode, 40e
... 5th dynode, 40f ... 6th dynode, 40g ...
7th dynode, 40h 8th dynode, 50 anode, 51 microchannel plate (MCP), 5
2 ... input side electrode, 53 ... output side electrode, 54 ... fluorescent screen, 5
Reference numeral 5: electrode, 56: fiber plate, 61: ohmic electrode, 62: Al _0.65 Ga _0.35 As, 63: undoped GaAs, 64: contact layer, 65: Schottky electrode, 100, 200: photomultiplier, 300: image intensifier tube.

Claims (8)

[Claims] 1. A semiconductor substrate made of Si, GaAs or GaP, and a p-type Ga _1-x formed on the semiconductor substrate.
A light absorption layer made of In _x N _y As _1-y or p-type Ga _1-x In _x N _y P _1-y and absorbing detected light to be detected to generate photoelectrons; and the light absorption layer And a carrier concentration of 1 × 10 ¹⁷
an electron transport layer made of p-type GaAs, p-type GaP or a mixed crystal thereof having a size of not less than cm ^-3 and diffusing photoelectrons generated from the light absorption layer to near the surface; and an alkali metal formed on the electron transport layer, Or a surface layer made of an oxide or a fluoride thereof and negatively reducing the electron affinity of the electron transport layer. 2. A semiconductor substrate made of Si, GaAs or GaP, and a p-type Ga _1-x formed on the semiconductor substrate.
A light absorption layer made of In _x N _y As _1-y or p-type Ga _1-x In _x N _y P _1-y and absorbing detected light to be detected to generate photoelectrons; and the light absorption layer And a carrier concentration of 1 × 10 ¹⁵
an electron transport layer made of p-type GaAs, p-type GaP or a mixed crystal thereof having a size of not less than cm ^-3 and diffusing photoelectrons generated from the light absorption layer to near the surface; and an alkali metal formed on the electron transport layer, Or a surface layer comprising an oxide or a fluoride thereof, which negatively reduces the electron affinity of the electron transport layer; and forming a Schottky junction with the electron transport layer formed on the electron transport layer. An electrode for applying a bias voltage so as to be positive with respect to the light absorbing layer. 3. A semiconductor substrate made of Si, GaAs or GaP, and a p-type Ga _1-x In _x N _y A formed on the semiconductor substrate.
a light-absorbing layer formed of s _1-y or p-type Ga _1-x In _x N _y P _1-y and absorbing light to be detected as a detection target to generate photoelectrons; and formed on the light absorbing layer. , Carrier concentration is 1 × 10 ¹⁵
an electron transport layer made of p-type GaAs, p-type GaP or a mixed crystal thereof having a size of not less than cm ^-3 and diffusing photoelectrons generated from the light absorption layer to near the surface; and an alkali metal formed on the electron transport layer, Or an oxide or a fluoride thereof, a surface layer which negatively reduces the electron affinity of the electron transport layer; and n-type GaAs, n formed on a part of the electron transport layer.
A contact layer made of GaP or a mixed crystal thereof and forming a pn junction with the electron transport layer; and a bias voltage formed on the contact layer so that the electron transport layer is positive with respect to the light absorption layer. A photocathode, comprising: 4. The semiconductor device according to claim 1, wherein the lattice constant of the semiconductor substrate, the lattice constant of the light absorption layer, and the lattice constant of the electron transport layer are equal to each other within a shift of 1% or less. The photocathode according to any one of claims 1 to 3. 5. The Ga _1-x In _x N forming the light absorption layer
_y The composition y of N in As _1-y or Ga _{1- x} In _x N _y P _1- y is
The photocathode according to claim 1, wherein 0 <y ≦ 0.2. 6. The forbidden band width of the semiconductor substrate and the forbidden band width of the electron transporting layer are both larger than the forbidden band width of the light absorbing layer. The photocathode according to 1. 7. A vacuum container having an entrance window through which light to be detected is incident, the interior of which is kept in a vacuum, and which is housed in the vacuum container facing the entrance window. 2. An electron tube, comprising: the photocathode according to claim 1; and an anode housed in the vacuum vessel and maintained at a positive potential with respect to the photocathode. 8. The electron tube according to claim 7, further comprising an electron multiplying unit housed in the vacuum vessel and multiplying photoelectrons from the photocathode by secondary electrons.